Gardaí are investigating a number of what are thought to be hoax calls made to emergency services this morning.
At approximately 7:30am, emergency services in Limerick received calls that a woman had entered the water at Thomond Bridge in the city.
Limerick City and County Fire and Rescue Service launched their rescue boat FireSwift alongside ground crews who performed searches the river.
Gardaí, and the Limerick Marine Search and Rescue Service, and a HSE ambulance crew, also all responded to the alert.
A source in the emergency services said they believed the 999 caller had removed the sim from their mobile phone, thus preventing gardaí from making direct contact with the person.
All measures are been looked at to try to track the caller.
"The call was determined to be a false alarm," said the source.
"Immediately after this incident, Limerick Fire and Rescue Service were alerted to a call to a car on fire in St Mary's Park," they added.
"This was also determined to be a hoax call."
Around 30 emergency service personnel responded to both alerts.
Three fire tenders with 12 firefighters including a five-man swiftwater rescue team on a boat responded to the river alert.
One fire tender with six firefighters on board responded to the "car fire" callout.
Gardaí at Henry Street are investigating.